IX THE MARKINGS OF ORGANISMS 205- 



Though there is no successional repetition in a 

 Vertebrate, the rule that parts occupying similar 

 positions tend to be similarly coloured holds good 

 here as in Invertebrates. The similarity seems, 

 however, here to have relation to position with refer- 

 ence to the median axis of the body only. A brief 

 study of birds' feathers affords very convincing proof 

 of this. Thus, though the secondary quills of one 

 wing in a bird showing complicated feather-markings 

 resemble those of the other wing, it will be found 

 that the quills are not all absolutely the same, but 

 form a graduated series, of which the first and last 

 members may differ very considerably. The usual 

 difference between the markings of the two sides 

 of the vane may be explained in wing-quills as due 

 to the unequal development of the two sides, but, 

 except in the case of the central rectrices, it is quite 

 as common in the tail-quills, in which the two sides 

 are equally developed. In short, it is a general fact 

 that in Vertebrates, where the coloration depends 

 upon the colours of the epidermal outgrowths, the 

 pattern has reference to the body as a whole, the 

 colours of the individual structures being completely 

 subordinated to that whole. 



As to the nature and meaning of patterns, there 

 can be little doubt that in simple organisms they are 

 closely related to segmentation, are expressions of 

 the same process. It has been dimly suggested by 

 various authors, but nowhere with such force and 

 eloquence as by Mr. Bateson, that both patterns and 

 segmentation may be purely mechanical phenomena, 

 and that " the perfection and symmetry of the pro- 

 cess, whether in type or in variety, may be an ex- 



